1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and particularly, to a rubbing method of an LCD device, using a magnetic field.
2. Description of the Related Art
With recent developments of various portable electronic devices, such as mobile phones, personal digital assistants (PDAs), and notebook computers, demand for light weight, thin profile, small flat panel display devices is increasing. Present research includes active development of flat panel display devices including liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and vacuum fluorescent display (VFD) devices. Of these different devices, LCD devices are actively being developed due to the simple mass-production techniques necessary to produce them, their simple driving systems, and high picture quality.
FIG. 1 is a cross sectional view of a liquid crystal display device according to related art. In FIG. 1, a liquid crystal display device 1 includes a lower substrate 5, an upper substrate 3, and a liquid crystal layer 7 formed between the lower and upper substrates 5 and 3. The lower substrate 5 is a driving unit array substrate and includes a plurality of pixels (not shown), wherein each pixel includes a driving unit, such as a thin film transistor. The upper substrate 3 is a color filter substrate and includes a color filter layer for implementing display color.
A pixel electrode and a common electrode are respectively formed on the lower substrate 5 and the upper substrate 3. In addition, an alignment layer for aligning liquid crystal molecules of the liquid crystal layer 7 is formed on the pixel electrode and on the common electrode. The lower substrate 5 and the upper substrate 3 are attached by a sealing material 9, and the liquid crystal layer 7 is formed therebetween. The liquid crystal molecules of the liquid crystal layer 7 are driven by a driving unit formed at the lower substrate 5, wherein a quantity of light transmitted through the liquid crystal layer 7 is controlled to display an image.
FIG. 2 is a flow chart of a method for fabricating a liquid crystal display device according to the related art. In FIG. 2, the fabrication process of the liquid crystal display device is roughly divided into a driving unit array substrate process for forming a driving unit at the lower substrate 5, a color filter substrate process for forming the color filter at the upper substrate 3, and a cell process.
In FIG. 2, a step S101 includes forming a plurality of gate lines and a plurality of data lines on the lower substrate 5 using the driving device array process for defining a plurality of pixel areas. The step 101 includes formation of thin film transistors, and driving devices that are connected to the gate lines and the data lines at the pixel areas. In addition, a plurality of pixel electrodes, each of which is connected to one of the thin film transistors through the driving device array process, are formed. The pixel electrode drives a liquid crystal layer when a signal is transmitted through the thin film transistor.
A step S104 includes formation of a color filter layer of R, G, and B colors, and formation of a common electrode on the upper substrate using the color filter process.
Steps S102 and S105 both include formation of alignment layers on the upper and lower substrates, wherein the alignment layers are rubbed to provide the liquid crystal molecules of the liquid crystal layer formed between the upper and lower substrates with an initial alignment and surface fixing force (i.e., pre-tilt angle and orientation direction).
A step S103 includes scattering a plurality of spacers onto the lower substrate for maintaining a uniform cell gap between the upper and lower substrates.
A step S106 includes formation of a sealing material along an outer portion of the upper substrate.
A step S107 includes attaching the upper and lower substrates together by compressing the upper and-lower substrates together.
A step S108 includes dividing the attached upper and lower substrates into a plurality of individual liquid crystal panels.
A step S109 includes injection of the liquid crystal material into the liquid crystal panels through a liquid crystal injection hole, wherein the liquid crystal injection hole is sealed to form the liquid crystal layer.
A step S110 includes testing the injected liquid crystal panel.
Operation of the LCD device makes use of an electro-optical effect of the liquid crystal material, wherein anisotropy of the liquid crystal material aligns liquid crystal molecules along a specific direction. Because control of the liquid crystal molecules significantly affects image stabilization of the LCD device, formation of the alignment layer is critical for fabricating an LCD device that produces quality images.
In general, the alignment layer forming process includes a printing process and a rubbing process. The rubbing process provides uniform alignment of the liquid crystal molecules to achieve a normal liquid crystal driving, and is a main factor contributing to uniform display characteristics.
FIGS. 3A and 3B show an alignment layer rubbing process. As show therein, in the alignment layer rubbing process, an alignment layer 101 made of polyimide is formed on a substrate 100 having several cells, each cell having a thin film transistor or a color filter. An ion blower 103 operates on the alignment layer 101, thereby removing static electricity, and thin pieces of ionic materials generated in the rubbing process from the alignment layer 101. In the rubbing process, a rubbing roll 102 having a rubbing cotton 105 is rotated in place, and the substrate 100 is moved to the right by using a stage 116 and a driving roller 117 so that the alignment layer 101 passes under the rubbing cotton 105. In such a manner, a pattern is formed on the surface of the alignment layer 101. Here, not only the alignment layer 101 but also other substrate parts come in contact with the rubbing cotton 105. And, a rubbing pattern of the alignment layer 101 is controlled by upwardly or downwardly controlling the rubbing roll 102 to constantly maintain a gap between the substrate 100 and the rubbing roll 102. However, a step is generated because of the difference in height between the substrate 100 and patterns such as thin film transistors that are formed on the substrate. Moreover, because it is formed on the entire thin film transistor pattern 130, the alignment layer 101 is also applied on the step generated by the thin film transistor pattern 130 on the substrate 100.
Moreover, if the rubbing cotton 105 comes in contact with an alignment layer, formed at a position where the thin film transistor pattern 130 is formed, after the rubbing cotton 105 contacts with the alignment layer that is formed at a position where the thin film transistor pattern 130 is not formed, the rubbing cotton 105 can become damaged and then scratch the alignment layer formed at a position where the step does not even exist. That is, fine damage of the rubbing cotton 105 can cause scratches on the alignment layer in the rubbing process. When the rubbing cotton 105 advances into an active region 170, such a defective rubbing frequently occurs. Once defective rubbing occurs, scratches are continuously made on the active region 170. In addition, defective rubbing occurs in both twisted nematic (TN) mode LCD devices and in plane switching (IPS) mode LCD devices, and, especially, the defect is worse in IPS mode LCD devices.
As so far described, the rubbing method using the conventional rubbing roll is disadvantageous in that the rubbing cotton can be damaged by a step of a pattern, thereby causing scratches on the alignment layer. In addition, in the rubbing process, alignment layer remnants are generated in a valley formed in the alignment layer, and dusts are caused to float by rubbing cotton naps generated at the rubbing cotton. The scratches or dusts are main factors causing stains on a screen.
In addition, the rubbing method according to the related art is disadvantageous because space utilization is degraded as the rubbing roll becomes large in response to a large substrate, and uniform rubbing is made difficult because of inconstant pressure applied to the substrate by the rubbing roll.